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Navigation:Geological Time Periods/Phanerozoic Eon/Mesozoic Era/Cretaceous Period/Maastrichtian Stage
The Maastrichtian is the final stage of the Late Cretaceous period, covering the duration of time from 72 - 66 million years ago. Flora & Paleoecology Maastrichtian flora include Metasequoia, a species of 60 meter tall fast-growing redwood. The genus has one living species. The extant (not extinct) genus of coniferous tree Araucaria is also found in many Maastrichtian formations. A detailed study of Alaskan rock formations dating to the Maastrichtian has revealed that the Maastrichtian arctic ecosystem had an average temperature of around 7-8 degrees Celsius, comparable to modern places like Stockholm or Helsinki. The study (link) also found that the climate was highly seasonal. North America North America has the most intensely studied Mesozoic rock formations and thus some very well-documented fossil ecosystems, some of which will be detailed below. During the Cretaceous, the Western Interior Seaway covered much of central North America and before the Maastrichtian this had divided North America in two; however, by the Maastrichtian the Western Interior Seaway had shrunk until it only reached up until about Canada's modern border. The Western Interior Seaway formed two distinctive parts of the continent, Laramidia in the west and Appalachia to the east, with the sea in the middle. Little is known about Appalachia's ecology, but Larimidia had extensive coastal floodplains along the length of most of the north-western shore of the Interior Seaway, which are believed to have been the ideal location for ancient river-filled forests. The fact that this region had lots of water and might have occasionally flooded provides ideal location for fossilization, and is the direct cause of two formations that are listed below - Hell Creek and the Lance Formation. The more southern parts of Larimidia, home to the Ojo Alamo formation and animals like Alamosaurus and Quetzalocatlus, were arid and much drier than the north. Along the western part of the subcontinent the Rocky Mountains were beginning their formation, leading to dry highland with very bad fossilization environments. Very little is known about these dry highlands. Hell Creek Formation (late Maastrichtian) The Hell Creek formation contains fossils from the last one million years before the asteroid impact and is spread out across parts of Montana, North Dakota, South Dakota and Wyoming. Its environment would have consisted of riverine forest, floodplain and beaches, providing an ideal fossilization environment. Fish Acipenser ''- a genus of sturgeon, still living today. ''Lepisosteus - a genus of gar (small, mostly freshwater fish group) Coriops Amphibians Opisthotriton - A prehistoric salamander Pterosaurs Quetzalcoatlus? - single pterosaur neck vertebra, probably belonging to Quetzalocatlus. Crocodylomorphs Borealosuchus - 3-meter crocodile, found across North America during the Late Cretaceous and Paleocene Brachychampsa - an alligator Thoracosaurus Turtles Compsemys Hoplochelys Trionyx Gamerabaena Lizards Obamadon - ''named after the US president, about 30 cm long, preyed on insects '''Mammals' Mesodma Alphadon Didelphodon ''- one of the largest Mesozoic mammals, 50-100 cm long ''Cimolodon Ankylosaurid dinosaurs Anyklosaurus Ceratopsian dinosaurs Triceratops - Tatankaceratops is most likely species of Triceratops Torosaurus - A horned dinosaur similar to Triceratops Leptoceratops -'' a small, basal ceratopsian '''Ornithopod dinosaurs' Edmontosaurus Thescelosaurus '' '''Pachycephalosaurid dinosaurs' Pachycephalosaurus - probably includes Dracorex and Stygimoloch Sphaerotholus - probably same genus as Prenocephale Ornithomimosaurian dinosaurs Struthiomimus - ''some species may have reached 4 meters '''Oviraptorosaurid dinosaurs' Anzu - newly discovered species Maniraptoran dinosaurs Avisaurus Archeroraptor - ''considered to be the sole dromaeosaur in Hell Creek ''Brodavis '' '''Tyrannosaurids' Tyrannosaurus '' Horseshoe Canyon Formation (early Maastrichtian) The Horseshoe Canyon Formation, located in southwestern Alberta, Canada, dates from the early Maastrichtian (about 72-67 million years ago). As the formation's history spans 5 million years, not all of the species lived at the same time. It is divided into 5 stratigraphic units, dating from different periods of the formation's history and allowing for very precise chronological dating for these animals. '''UNIT 1 (73 - 71 mya)' Epichirostenotes '' ''Pachyrhinosaurus Ornithomimus '' ''Edmontosaurus '' ''Anchiceratops Pachycephalosaur (previously known as Sphaerotholus) UNITS 2-3 (71 - 70 mya) Ornithomimus '' ''Edmontosaurus Edmontonia Anodontosaurus Parksosaurus '' ''Albertosaurus UNIT 4 (70 - 68,5 mya) Ornithomimus '' ''Anodontosaurus Albertosaurus Saurolophus Hypacrosaurus '' ''Albertonykus '' ''Struthiomimus - only one species present, currenlty unnamed Atrociraptor '' '''UNIT 5 (68,5 - 67 mya)' Albertonykus Hypacrosaurus Eotriceratops Other dinosaurs known from this formation include Richardoestesia ''and ''Arrhinoceratops. Lance Formation (mid to late Maastrichtian) The Lance Formation is an exceptionally diverse formation that dates from 69 to 66 million years ago and is located in modern-day Wyoming. During the Maastrichtian the area had a subtropical climate with barely no cold season. The Lance Formation existed at the edge of the Western Interior Seaway which, from the Early Cretaceous to the Campanian, split North America into three parts; however, by the time of the Lance formation it had shrunk in size to an area covering Mexico, Texas, New Mexico, Colorado, Oklahoma, Nebraska, South Dakota and parts of Wyoming (Map) The environment of the Lance formation is thought to be similar to that of Hell Creek, with floodplains and forests. Non-avian Coelurosaurs Pectinodon Richardoestesia Struthiomimus Tyrannosaurus '' '''Avian Coelurosaurs (birds)' Ceramornis Cimolopteryx Graculavus Lonchodytes Palintropus Potamoris Ankylosaurids and nodosaurids Ankylosaurus Edmontonia Other Ornithischians Leptoceratops Nedoceratops Pachycephalosaurus '' ''Triceratops Edmontosaurus Thescelosaurus '' Asia Africa Madagascar As it is today, the Madagascar of the Late Cretaceous was an island, having separated from the island of India earlier on it geologic history. Both would have been drifting northwards as during the Maastrichtian Madagascar was still around ten degrees latitude more to the south than it is today. Madagascar's environment is believed to have been strongly seasonal and semi-arid towards the interior, though with floodplains and tidal flats along the shore. ''Majungasaurus ''and ''Beelzebufo ''were certainly inhabitants of these coastal habitats. '''Dinosaurs' Majungasaurus - ''lowly built abelisaurid theropod ''Rapetosaurus - moderately large 15 meter sauropod Rahonavis - A small dromaeosaur Masiakasaurus - A small abelisaurid Crocodylomorphs Araripesuchus Simosuchus Mahajangasuchus Amphibians ''Beelzebufo - ''largest known frog, up to 40 cm